A sensor system with position sensors and/or direction of rotation sensors is frequently used to detect position, direction of rotation, rotational speed and/or in order to detect a case of trapping of a motor-operated adjustment device of a motor vehicle. Such a sensor system, which operates according to the transmission and reception principle, usually requires, in addition to a receiver in the form of, for example, a Hall sensor or a coil, a transmitter in the form of a magnetic disk or a ring magnet with a number of magnet poles, i.e. with at least one north pole and one south pole.
In the case of a rotating drive or in the case of a linear adjustment such as, for example, an adjustment of the seat, in order to achieve a constant adjustment speed over the adjustment path, stringent demands are frequently made of the resolution of the sensor system in order, in particular in conjunction with a trapping protection system, to permit reaction times which are as short as possible.
For this purpose, DE 198 35 091 C1 discloses a method for performing open-loop and closed-loop control of motor-operated adjustment devices in motor vehicles. In this context, use is made of a sensor system with a signal transmitter which is connected to the drive shaft of a drive motor of the adjustment drive and is in the form of a multi-pole magnet which performs the transmitter function, and with a sensor in the form of a magneto-sensitive element. An electronic unit serves to evaluate the sensor signals.
In an embodiment according to WO 03/019751 A1, a ring magnet which performs the transmitter function is fitted onto the drive shaft of a commutator motor, and a Hall sensor which is connected to an electronic evaluation system is disposed opposite said ring magnet in a contactless fashion. Owing to the Hall effect, the receiver-end sensor supplies, during each revolution of the motor shaft, a number of signal pulses which corresponds to the number of the magnetic poles of the ring magnet which rotates with the motor shaft. By means of the electronic evaluation system which is connected downstream of the sensor it is possible to determine the direction of rotation and the rotational speed and therefore in turn the engine torque by reference to the sequence of individual signal pulses and from the period length and the pulse length. From the latter it is possible in turn to determine the current position of an adjustment element, for example of a window pane, which is moved by the adjustment drive, and also to detect a case of trapping.
In an alternative system in which a DC-fed rod armature motor is generally used, it is possible to evaluate via a current ripple which is caused by the commutation process of the drive motor to determine the rotational speed, direction of rotation and adjustment position.
The invention is based on the object of achieving the highest possible degree of integration of the adjustment drive and sensor system.
This object is achieved according to the invention by means of an adjustment drive of a motor vehicle, having a drive motor which has a motor magnet which generates a magnetic exciter field or exciter main field, and a motor armature which is rotatably arranged between the magnet poles of said motor magnet, in order to increase the integration of a sensor system, in particular in order to detect a position, the direction of rotation, a case of trapping or change in a rotational speed a magneto-sensitive sensor is positioned in such a way that it senses a change in the magnetic flux density of the exciter main field during a revolution of the armature.
Accordingly, the adjustment drive has a drive motor and a sensor which is preferably integrated into its exciter main field. In order to generate the exciter main field, the drive motor preferably comprises a permanent magnet on the stator side and a motor armature which is rotatably arranged expediently between its two magnet poles. The motor armature has a number of armature teeth or poles with armature grooves between them. In principle an electromagnet can also be used as the motor magnet. In an expedient use of a permanent magnet as a motor magnet, the armature teeth are provided with a motor winding which can be energized. The adjustment drive serves to drive an adjustment element of the motor vehicle, in particular of a window pane, of a seat, of a tailgate or of a sunroof.
The magnetic sensor is preferably a Hall sensor. The position of the magnetic sensor is determined by virtue of the fact that it is always subject to the stationary exciter main field. As a result, the sensor already operates at a fixed working point with a corresponding signal base level in the form of the voltage or Hall voltage which can be tapped at the sensor side as a result of the galvano-magnetic effect, of which the Hall effect is an example. During a revolution of the armature of the motor, the sensor detects a change in the magnetic flux density of the exciter main field owing to alternately varying air gap inductions and/or alternately changing magnetic resistances. In other words, on the basis of a signal base level which serves as a working point the sensor also senses changes in a parameter of the magnetic field which is generated by the motor magnet owing to circumferential sections of the motor armature which change in the circumferential direction with alternately changing different magnetic properties.